The invention generally relates to a circuit configuration for the selective switching of read signals of one of at least two magnetic systems of a multiple magnetic head onto a common read channel of a magnetic layer memory. More particularly, the invention relates to a circuit configuration for the selective switching through of read signals of one of at least two magnetic systems of a multiple magnetic head onto a read channel of a magnetic layer memory using preamplifiers connected both to one of the magnetic systems and to a selecting device.
In magnetic layer memories, a magnetic head, which is stationary in its operating state, is used for storing or reading information, and a magnetic storage medium (e.g., a magnetic tape) is moved with respect thereto. In the relevant art, numerous magnetic head constructions are known which are matched to their intended uses.
In the simplest case, the magnetic head comprises a single magnetic system with a magnetic core forming a magnetic gap and a magnetic or field coil wound around the core for at least two operating functions; read and write; as well as, optionally, erasure of stored information. However, particularly in the case of magnetic layer memories, it has proved advantageous to provide individual, partial magnetic heads for each of these different operating functions.
Considering the magnetic tape feed direction, a read head frequently is positioned between a write head and an erasure or erase head. Such a magnetic head construction not only makes it possible to specifically optimize the individual partial heads with respect to their functions, but the construction also permits a check read of information recorded immediately preceding during the writing process while it is still taking place. Such a magnetic head formed from partial magnetic heads can be referred to as a combined magnetic head or a read/write head.
Particularly in the case of magnetic tape memories, it is also known to use multiple magnetic head structures. The term "multiple magnetic head" is used to designate a magnetic head which has a plurality of magnetic systems positioned transversely with respect to the feed direction of the associated tape and which are in each case spatially associated with respect to a recording track on the tape. Such a multiple magnetic head makes it possible either to simultaneously write information in parallel in several information tracks or to simultaneously read out information from several information tracks.
However, even in those situations in which a writing or reading process is carried out only for a single information track, a correspondingly constructed multiple magnetic head can still be advantageous, because it, for example, can permit the storage processes for both magnetic tape feed directions. Based on an axis aligned at right angles to the longitudinal direction of the tape, at least two magnetic systems are placed adjacent to each other, each magnetic system case containing at least one writing and one reading partial head; and, optionally, an erase head. The write and read partial heads of these two magnetic systems are mutually transposed with respect to their positions in the direction of the tape longitudinal axis. With such a multiple magnetic head, this arrangement makes it possible to store information with a directly following check read in both feed directions of the magnetic tape. On the basis of this principle a plurality of multiple magnetic head constructions are conceivable involving the juxtaposing of a plurality of magnetic systems at right angles to the longitudinal direction of the magnetic tape.
The different constructions of multiple magnetic heads can provide special advantages with respect to positioning processes during the operation of magnetic tape memories or can be favorable in connection with tracking or track holding. However, the details of the described basic constructions of multiple magnetic heads are not most important herein. Instead, importance attaches to the selection problem which arises if and when, with such a multiple magnetic head, information is only read out of a selected information track and prepared in a read channel for the recovery of the information track and prepared in a read channel for the recovery of the information stored in this information track.
In principle this means that in the operating state "read", read signal voltages are simultaneously induced in all the partial read heads of the multiple magnetic head during the overflow of associated information tracks. However, only the read signals of the instantaneously selected information track are to be fed into the read channel and processed for the recovery of the stored information. For this it is necessary to have a selecting device, which can be referred to as a channel switch.
Normally read signals supplied by a magnetic system are initially preamplified and then further processed. It is obvious to place the channel switch either directly between the individual magnetic systems and a common preamplifier or to provide for each magnetic system an individual preamplifier and to install the channel switch between the parallel outputs of the plurality of preamplifiers and the inputs of one read channel. Such a solution involves considerable effort and expenditure and is also relatively complicated due to the high impedance values which have to be taken into account. Due to the low useful signal voltages on the input side of the channel switch, among other things, special precautions must be taken with respect to undesirable crosstalk of the unselected magnetic systems on the circuit of the selected magnetic system, because the channel switch must only selectively switch through the read signals supplied by the selected magnetic system having a lower signal amplitude than the useful signals.
Another important problem is the difficulty of providing an adequate common-mode rejection in order to achieve a desired signal-to-noise ratio in the switched through read signals. However, if individual preamplifiers are provided and the channel switch is arranged downstream thereof, the actual channel switch must process higher power levels and must consequently have a more complicated construction.